This invention relates, in general, to programmable read only memories (PROM) and more particularly, to an erase detector for those programmable read only memories which are eraseable.
Read only memories are well known and widely used in digital systems. More recently, programmable read only memories (PROM) have come into use. Some of these memories are programmable by the use of high voltage to program a predetermined cell within the memory after the memory is made. The programmed memories can also be altered or erased. Some times the erasure is accomplished by exposure to radiation such as ultraviolet radiation.
One of the conveniences of this type of memory is that it can be programmed after it is manufactured instead of requiring programming by a mask operation during the manufacturing process. Many times once the memory is programmed it is desirable to maintain the program without modifications, and in such cases it is important to determine whether the data within the memory has been tampered with, altered, or erased.
Accordingly, it is an object of the present invention to provide a new and improved erase detector for a programmable read only memory.
Another object of the present invention is to provide a method for detecting whether a programmable read only memory has been erased.
Yet a further object of the present invention is to provide a substantially fool-proof circuit for determining whether a programmable read only memory has been erased.